The present invention relates to a parallel-serial translator, and more in detail to a device, which translates electric signals inputted in parallel into parallel-serial-translated optical signals to send them to an optical waveguide.
For a computer, and in particular for a computer called a vector computer, it is extremely important for improving the performance of the computer to raise the capacity (amount of data which can be transmitted per unit time) of a data interconnecting line disposed between a main storage and a vector processor. Since the main storage has, in general, a speed lower than that of the vector processor, in many cases, in order to increase the transmission capacity the computer is so constructed that the main storage is divided into a plurality of memory banks driven parallelly, which can be accessed independently from each other (it is called interleave). Further, the speed of the vector processor is increased every time a new model is put on the market. Therefore, an increase in the speed of memories constituting the main storage cannot follow the increase in the speed of the vector processor. For this reason, the newer the model is, the greater the number of memory banks driven in parallel is. Although the number of memory banks is about 512 at present, it is thought that increases in the future such as 1024, 2048, etc. is likely.
When the number of memory banks increases, it becomes important to reduce the size of the interconnecting line connecting the main storage with the memory banks. For example, when data signal lines, each of which has a data width of 8 bytes (64 bits), are taken out from 512 memory banks as in a vector computer indicated in FIG. 1, 32768 data signal lines are connected between the main storage and the vector processor. Even if it is supposed that the cross-section of one signal line is as small as 1 mm.sup.2, an area of about 18 cm square is required for connecting all the data signal lines. This area is almost identical to that of an LSI mounting module constituting the vector processor. In order to increase further the number of memory banks, it is necessary to increase the capacity of the interconnecting line and to decrease the size thereof. A decrease in the size of the interconnecting line is important also for locating the vector processor closely to the main storage to shorten transmission time.
For increasing the capacity of the interconnecting line and decreasing the size thereof a method is known, by which a plurality of signals are parallel-serial-translated to be transmitted through one signal line (time slice multiplexing, hereinbelow in the present specification this process is sometimes abbreviated to P/S translation) and further optical fibers are used as a transmission medium, which has a smaller diameter and a higher transmission bit rate than a coaxial cable.
As an example therefor, there is known a transmitting device for great distance communication utilizing optical fibers used in practice in the field of communication. Here, FIG. 2 shows an example of construction of a vector computer, in which data read-out from a memory bank constituting the main storage are translated into an optical serial signal by using the parallel-serial translating technique used in the field of communication, which are transmitted to a vector processing unit. In order to simplify the explanation, here it is supposed that the data width is 8 bits and only signals concerning processing for reading out main storage data are described therein. FIG. 3 shows operation timing therefor. A vector processing unit 220 transmits an access control signal responding to an address to be accessed to a predetermined memory bank. The selected memory bank 241 holds data signals 2 read-out from the memory in registers 61 to 68 by switching-over selectors 51 to 58 in synchronism with a setup signal 1 after having started processing for reading out data at predetermined addresses by using the access control signal 8 and takes out the signals one after another in synchronism with a clock signal 5 while shifting them bit by bit, which signals are converted into optical signals in an electro-optical signal converter 20 to generate an optical output signal 3. A vector processor selects optical signals sent from the memory bank, responding to predetermined addresses and then returns the optical serial signals to electric parallel signals, which are transmitted to the vector processing unit. Since it can be thought that an optical serial signal-electric parallel signal translator 232 effects reverse translation with respect to the electric parallel-optical serial signal translator indicated in FIG. 3 and therefore it can be easily analogized therefrom, explanation of the contruction and the operation thereof will be omitted.
In this construction, since an electric parallel-serial translator 6 and an electric-optical signal converter 20 incorporating shift registers 61 to 68 are added to each of the memory bank, it is necessary to decrease the size thereof.
As an example for making these shift registers 61 to 68 unnecessary, JP-A-62-10934 discloses a parallel-serial translator, which translates parallel data into serial data by utilizing transfer delay of optical data in an optical fiber. However, in JP-A-62-10934, although a construction for translating optical data inputted in parallel into serial optical data is disclosed, no concrete construction is disclosed for indicating how the parallel optical data are obtained, starting from the electric signal data inputted in parallel.
As another example, in which the transfer delay of optical data in the optical fiber is used, there is known JP-A-1-256846. However, JP-A-1-256846 discloses only a technique, by which optical packet signals coming one after another through a plurality of input lines are arranged in series in optical fibers serving as output lines by switching-over them by means of an N.times.M spatial switch and indicates no concrete construction indicating how the parallel optical data can be obtained from the electric signal data inputted in parallel.
Further, in either one of the literatures described above, no attention is paid to decreasing the size of the parallel-serial signal translator. A high speed and small size parallel-serial signal translator, i.e. electric signal-optical signal converting device, is required for utilizing optical waveguides such as optical fibers between the main storage and the vector processor and converting the electric signal data inputted in parallel into the serial optical data to transmit them.